I don't know what to make of the new manager.
这位新经理，我不知道怎么评价他才好。
I don't know what you're on about.
我不懂你在谈什么。
I don't know how you can say things like that.
真想不到你怎么会说出这种话来。
I don't know how she puts up with him.
我不明白她怎么受得了他。
I don't know if I can come but I'll try.
我不知道是否能来，但我尽可能来。